EP2291423A1

EP2291423A1 - Block copolymer containing a photoactive monomer bearing a photoisomerizable group, use thereof in a 3d optical memory

Info

Publication number: EP2291423A1
Application number: EP09766035A
Authority: EP
Inventors: Chistophe Le Crom; Sylvain Bourrigaud; Sylvie Cazaumayou
Original assignee: Arkema France SA
Current assignee: Arkema France SA
Priority date: 2008-05-27
Filing date: 2009-05-15
Publication date: 2011-03-09
Also published as: FR2931827A1; US20110129636A1; WO2009153473A1; KR20110021975A; JP2011522917A

Abstract

The invention relates to a block copolymer comprising: at least one soft block A having a Tg between -55°C and 0°C, preferably between -40°C and -1°C and at least one block B comprising at least one photoactive monomer bearing a photoisomerizable chromophore. The photoactive monomer has the formula (I) : in which: X denotes H or CH3-; G denotes -O-C(=O)-, -C(=O)-O-, a substituted or unsubstituted phenyl group or else -NR-C(=O)-, NR being connected to L and R being H or a C1-C10 alkyl group; L denotes a spacer group; CR denotes a photoisomerizable chromophore. The block copolymer makes it possible to obtain a 3D optical memory. The invention also relates to this 3D optical memory.

Description

Block copolymer containing a photoactive monomer carrying a photoisomerisable group, its use in a 3D optical memory

[Technical domain] The considerable development of digital information systems has led to a growing need for large, compact data storage units that provide long-term data preservation for up to 50 years. Optical storage is one of the technologies that is available for storing data (see SPIE, "Conference on nano- and micro-optics for information systems," August 4, 2003, paper 5225-16).

The technology that is contemplated in the present invention is more particularly that of 3-D optical storage as described in international applications WO 01/73779 and WO 03/070689 and in Japanese Journal of Applied Physics. , Flight. 45, No. 28, 2006, pp. 1229-1234. It is based on the use of a photoisomerizable chromophore which is in two interconvertible thermodynamically stable isomeric forms under the effect of a light irradiation of appropriate wavelength. When no data has yet been recorded, one of the two forms has a majority. For data writing, this isomeric form is converted to the other by light irradiation having an appropriate wavelength. The conversion may result from a direct or indirect optical interaction (eg multiphoton).

The present invention relates to a polymer for optical data storage in 3D. It also relates to the material obtained from this polymer as well as to the optical memory in 3D, in particular in disk form.

[Technical problem]

In the application WO 03/070689, the chromophores are attached to a polymer through the (co) polymerization of monomers carrying said chromophores. The application WO 2006/075327 also teaches the interest in increasing the concentration of chromophores so as to improve the recording sensitivity of the optical memory. However, when the concentration of monomers carrying chromophores increases, the mechanical properties of the polymer are affected and the material obtained is either too fragile or too soft to be manipulated easily. The need therefore exists to develop a rigid material that can be used in the field of 3D optical storage having good readability and data writing.

The Applicant has found that the block copolymers as defined in claim 1 or the mixture as defined in claims 25 to 27 meet this need.

[Prior Art] US Patent 5023859 discloses an optical memory based on the use of a polymer carrying a photosensitive group of stilbene, spiropyran, azobenzene, bisazobenzene, trisazobenzene or azoxybenzene type. The polymer may be a block polymer but the exact nature of this block polymer is not specified.

The international application WO 01/73779 describes an optical storage unit in which the information is stored thanks to the cis- / trans transition of a molecule (chromophore) having a C = C double bond. The molecule may in particular be a diarylalkylene of formula Ar ₁ R ₁ C = CR ₂ Ar ₂ which may be linked to a polymer.

International application WO 03/070689 describes a polymer carrying a chromophore of diarylalkylene type. The polymer may be a polyalkylacrylate or a copolymer of the polyalkylacrylate, especially a copolymer with styrene. It may also be polymethyl methacrylate. It is not specified that it may be a block copolymer or that the chromophore is present in one of the blocks in particular.

International application WO 2006/075328 discloses compounds of the diarylalkylene type that can be used in optical storage.

International application WO 2006/075327 discloses polymers having diarylalkylene type chromophores. Cooperative effect is mentioned when the chromophore concentration increases.

International application WO 2006/075329 describes a 3D memory in disk form. [Brief description of the invention]

The invention relates to a block copolymer comprising:

At least one soft block A having a T ₉ between -55 ° C. and 0 ^° C., preferably between -40 ^° C. and -1 ° C.,

At least one block B comprising at least one photoactive monomer carrying a photo-isomerizable chromophore.

According to the invention, at least one soft block A or at least one block B means that the block copolymer can comprise one or more blocks A and one or more blocks B.

In addition, the block B can comprise one or more photoactive monomers associated with another monomer. In particular, in addition to the photoactive monomer, the block B may advantageously comprise a cooperative effect monomer.

The photoactive monomer has the formula (I):

CR-LG-C = CH ₂

I x (i) in which:

X is H or CH ₃ -;

G denotes -OC (= O) -, -C (= O) -O-, a phenyl group, substituted or unsubstituted by one or more substituents, or -NR-C (= O) -, NR being connected to L and R being H or a C ₁ -C ₁₀ alkyl group; • L denotes a spacer group;

• CR denotes a photo-isomerizable chromophore.

The block copolymer makes it possible to obtain a 3D optical memory. The invention also relates to the mixture comprising the block copolymer and a polymer which is a thermoplastic, a thermoplastic elastomer or a thermosetting and a 3D optical memory comprising the block copolymer or the polymer mixture. The invention also relates to the use of a block copolymer or a mixture of block copolymers as described above for performing optical data storage. - AT -

[Detailed description]

T ₉ denotes the glass transition temperature of a polymer, measured by DSC according to ASTM E1356. The T ₉ of a monomer is also referred to as the T ₉ of the homopolymer having a number-average molecular weight M _n of at least 10,000 g / mol, obtained by radical polymerization of said monomer. Thus, it will be said that ethyl acrylate has a T ₉ of -24 ° C because the ethyl homopolyacrylate has a T ₉ of -24 ° C. All percentages are by weight unless otherwise indicated.

The term "photoactive monomer" is understood to mean a monomer carrying a photo-isomerizable CR chromophore group. The chromophore exists in two isomeric forms, for example cis / trans. The conversion from one form to another takes place under the action of a light irradiation of appropriate wavelength.

According to the invention, the photoactive monomer has the formula (I):

CR-LG-C = CH ₂

I x (i) in which:

X is H or CH ₃ -;

G denotes -OC (= O) -, -C (= O) -O-, a phenyl group, substituted or unsubstituted by one or more substituents, or -NR-C (= O) -, NR being connected to L and

R being H or a C ₁ -C ₁₀ alkyl group;

• L denotes a spacer group;

• CR denotes a photoisomerizable chromophore.

The spacer group L has the function of improving the freedom of movement of the chromophore with respect to the copolymer chain so as to promote the conversion of the chromophore from one form to another. This improves the capacity and speed of reading. Preferably, L is chosen such that G and CR are connected to each other by a sequence of 2 or more atoms which are linked together by covalent bonds. L can be chosen for example from groups (CRiR ₂ ) _m! O (CRIR ₂₎ m, (OCRiR ₂₎ _m or (SCRiR ₂₎ _m wherein m is an integer greater than 2, preferably between 2 and 10 and R ₁ and R ₂ independently denote H, halogen or alkyl or aryl. Preferably, R 1 and R ₂ denote H. The chromophore CR is preferably of the diarylalkylene type existing in cis and trans isomeric forms. It may be one of the chromophores disclosed in WO 01/73779, WO 03/070689, WO 2006/075329 or WO 2006/075327. Preferably, chromophore CR is chosen so that the energy barrier for isomerization is greater than 80 kJ / mol. Indeed, it is desirable that the isomerization is a very slow process at room temperature to avoid a loss of recorded data.

Preferably, the photoactive monomer has the formula (II):

in which :

Ar ₁ and Ar ₂ denote aryl groups, optionally substituted with one or more substituents;

W ₁ and W ₂ are chosen from the groups H, -CN, -COOH, -COOR ', -OH, -SO ₂ R', -NO ₂ , R 'being a C ₁ -C ₁₀ alkyl or aryl group; .

The chromophore corresponds to the grouping Ar ₁ W ₁ C = CW ₂ Ar ₂ . L is linked by covalent bonds to Ar ₂ as well as to G. Ar ₁ and Ar ₂ denote aryl groups, substituted or unsubstituted. They are chosen for example independently of one another from phenyl, biphenyl, anthracene or phenanthrene groups. Substituent (s) are selected potential (s) from: H, C ₁ -C ₁₀ alkyl, NO _2, halogen or alkoxy, C ₁ - C _10, NR "R"'with R "and R'" being H or C ₁ -C ₁₀ alkyl. Ar ₁ is attached to the C = C double bond of the chromophore. Ar ₂ is attached to the C = C double bond of the chromophore as well as to the L group.

Preferably, G is -O-C (= O) - or the phenyl group C ₆ H ₄ , that is to say that the photoactive monomer has the formula: wi Ar ₂ -L-O-C (= 0 ) - C = CH ₂

Ar ₁ W ₂ (H,)

OR

Preferably, Ar ₁ is a phenyl or biphenyl group and Ar ₂ is a phenyl or biphenyl group, each of the phenyl and / or biphenyl groups may be optionally substituted by one or more substituents, that is to say that the chromophore has for formula (V) or (VI):

The optional substituents may be for example H, aryl, alkyl CRCI _0, NO _2, halogen or alkoxy CRCI _0.

In a preferred form, W ₁ and W ₂ are H or CN, Ar ₂ is phenyl or biphenyl, Ar ₁ is phenyl or biphenyl substituted para to R ₅ O- or R ₅ S-. R ₅ denotes an alkyl or aryl group, substituted or unsubstituted. Preferably, R ₅ is a C ₁ -C ₄ alkyl group. R ₅ may be, for example, a methyl, ethyl, propyl or butyl group. For example, it may be the chromophore of formula (VII):

According to another preferred form, W ₁ and W ₂ denote H or CN, Ar ₂ is a phenyl or biphenyl group, Ar ₁ is a biphenyl group substituted by R ₅ O- or R ₅ S-. For example, it may be the chromophore of formula (VIII):

The following two monomers denoted MeAA or MeMMA are very particularly preferred:

Indeed, they have good optical characteristics for writing and reading (see in this connection, Japan Journal of Applied Physics Vol.45, No. 28, 2006, pp.1229-1234): the trans isomer presents a greater fluorescence than cis; the trans isomer has a large biphotonic absorption cross section; the Stokes shift ("Stokes shift") is greater than 100 nm (little overlap between the absorption and emission spectra with peaks at 375 and 485 nm respectively).

They are also easily copolymerizable with a wide range of monomers, in particular by the controlled radical polymerization technique. Finally, they exhibit great stability because the isomerization energy barrier is greater than 80 kJ / mol. Chromophores which have a low overlap, i.e. <35% or even better <20%, between the absorption and emission spectra are preferred (see, on this, page 22 of WO 2006/075327). . This makes it possible to increase the concentration of the chromophore and thus to promote the cooperative effect without impairing the quality of the signal during the reading. The overlap depends on both the Stokes displacement and the peak width. The overlap is defined as the absorbed emission percentage for a solution of the 0.01 M chromophore in a 1 cm passage vessel. Preferably, the Stokes shift is> 100 nm. The measurement of Stokes displacement is well known to those skilled in the art: reference may be made in particular to the document DEKKER encyclopedia of nanoscience and nanotechnology by James A. Schwartz et al., Published: illustrated published by CRC Press, 2004, pages 4014 and following or encyclopedia of Optical Engineering: Las-Pho, pages 1025 and following, Ronald G. Driggers, illustrated edition published by CRC Press, 2003. This displacement is measured by comparing the emission spectra and absorption chromophore in a commercial spectrofluorometer. This displacement represents a physical property of a chromophore and is independent of the type of spectrofluorimeter used.

The invention is not limited to the particular chromophores of the diarylalkylene type but can also be applied to other photoisomerizable chromophores, not including stilbene, spiropyran, azobenzene, bisazobenzene, trisazobenzene or azoxybenzene groups. A list of chromophores useful in the invention is found in the following documents US 5023859, US 6875833 and US 6641889.

The term "cooperative effect monomer" means a compound of formula (VIII):

-LG- Ar ₃ C = CH ₂ I x (VIII) in which: • X, G and L have the same meanings as for the photoactive monomer;

Ar ₃ denotes an aromatic group which may or may not be substituted by one or more substituents. This cooperative-effect monomer interacts with the chromophore and / or enhances the cooperative effect between the chromophores themselves, thereby improving the writing speed. An interpretation of the cooperative effect is that the monomer modifies the microenvironment of the chromophore and promotes photo-isomerization.

The substituent for formula (VIII) is selected from: (i) halogens;

(ii) -COOY, -CONYY ', -OY, -SY or -C (= 0) Y, Y and Y' denoting a H or alkyl group Ci-Ci ₀ (Ni) - CYY'Y ", Y, Y ', Y "denoting an H or C ₁ -C _{10 (} C ₁ -C ₄₎ alkyl group, Y, Y', Y" denoting an H or C ₁ -C ₁₀ alkyl group;

Advantageously, Ar ₃ is a phenyl group. Advantageously, the halogen group is chlorine. Even more advantageously, Ar ₃ is chosen from the following groups:

By way of examples, the following hindered monomers can be used:

C = CH ₂ phenoxy ethyl methacrylate (PEMA) phenoxypropyl methacrylate (PPMA) phenoxy ethyl acrylate (PEA) phenoxypropyl acrylate (PPA)

Cl TCLPa

2,4,6 trichlorophenoxy propyl methacrylate 2,4,6 trichloro phenoxypropyl acrylate

For block A, it can be "rigid" or "soft". Block A is considered "rigid" when its glass transition temperature is above room temperature, 25 °. Block A is considered "soft" when its glass transition temperature is below 25 ° C. It has according to the invention a T ₉ between -55 ° C and 0 ^° C, preferably between -40 ^° C and -1 ° C and is therefore soft. Preferably, it also has a number average mass Mn> 1000 g / mol, advantageously> 5000 g / mol, preferably> 10000 g / mol.

One of the functions of the soft block A is to obtain sufficient mechanical strength of the memory storage material.

The soft block A is obtained from the polymerization of at least one vinyl, vinylidene, diene, olefinic, allylic or (meth) acrylic monomer such that the combination of monomers leads to a Tg of the block A <20 ^° C. and in particular at most equal to 0 ° C, for example between -30 ° C and -3 ° C. These monomers are chosen more particularly from vinylaromatic monomers such as styrene or substituted styrenes, especially alpha-methylstyrene, acrylic monomers such as acrylic acid or its salts, alkyl acrylates, cycloalkyl acrylates or aryl acrylates. such as methyl, ethyl, butyl, ethylhexyl or phenyl acrylate, hydroxyalkyl acrylates such as 2-hydroxyethyl acrylate, ether alkyl acrylates such as acrylate methoxyethyl, alkoxy- or aryloxy-polyalkylene glycol acrylates such as methoxypolyethylene glycol acrylates, ethoxypolyethylene glycol acrylates, methoxypolypropylene glycol acrylates, methoxy-polyethylene glycol-polypropylene glycol acrylates or mixtures thereof, aminoalkyl acrylates such as 2- (dimethylamino) ethyl acrylate (ADAME), fluorinated acrylates, silylated acrylates, phosphorus acrylates such as phosphorus acrylates alkylene glycol, methacrylic monomers such as methacrylic acid or its salts, alkyl, cycloalkyl, alkenyl or aryl methacrylates such as methyl methacrylate (MMA), lauryl, cyclohexyl, allyl, phenyl or naphthyl, hydroxyalkyl methacrylates such as methacrylate of 2-hydroxyethyl or 2-hydroxypropyl methacrylate, ether alkyl methacrylates such as 2-ethoxyethyl methacrylate, alkoxy- or aryloxy-polyalkylene glycol methacrylates such as methoxypolyethylene glycol methacrylates, ethoxypolyethylene glycol methacrylates, methoxypolypropylene glycol methacrylates, methoxy-polyethylene glycol-polypropylene glycol methacrylates or mixtures thereof, aminoalkyl methacrylates such as 2- (dimethylamino) ethyl methacrylate (MADAME), fluorinated methacrylates such as 2,2,2-methacrylate; trifluoroethyl, silylated methacrylates such as 3-methacryloylpropyltrimethylsilane, phosphorus methacrylates such as alkylene glycol phosphate methacrylates, hydroxyethylimidazolidone methacrylate, hydroxyethylimidazolidinone methacrylate, 2- (2-oxo) methacrylate 1-imidazolidinyl) ethyl, acrylonitrile, acrylamide or substituted crylamides, substituted 4-acryloylmorpholine, N-methylolacrylamide, methacrylamide or methacrylamides, N-methylolmethacrylamide, methacrylamido-propyltrimethylammonium chloride (MAPTAC), itaconic acid, maleic acid or its salts, maleic anhydride, alkyl or alkoxy- or aryloxy-polyalkylene glycol maleates or hemimaleate, vinylpyridine, vinylpyrrolidinone, (alkoxy) poly (alkylene glycol) vinyl ether or divinyl ether, such as methoxy poly (ethylene glycol) vinyl ether, poly (ethylene glycol) divinyl ether, olefinic monomers, among which mention may be made of ethylene, butene, hexene and 1-octene as well as fluorinated olefinic monomers, and vinylidene monomers, among which may be vinylidene fluoride, alone or in a mixture of at least two monomers mentioned above.

The soft block A is preferably obtained from styrene and / or (meth) acrylic monomer (s) and / or alkyl acrylate. Advantageously, the block A comprises, as the main monomer (s), styrene and / or MMA and / or butyl acrylate or ethyl hexyl acrylate. Preferably, it comprises at least 50% of butyl acrylate or 2-ethylhexyl acrylate.

Block A is intended to confer the mechanical properties of strength and / or rigidity of the finished material.

According to the process for preparing the block copolymer, the soft block A may contain, in addition to the above monomers, monomers (s) composing the block (s) B, especially photoactive monomer or cooperative-effect monomer. In fact, in the case where the block B is prepared during a first stage, the block A may contain residues of the monomer (s) constituting the block B. Thus, if this (s) monomer (s) residual (s) no polymerization (s) is (are) present in the reaction mixture when starting the polymerization leading to the (x) block (s) A, the block (s) A may comprise or monomers (s) initially introduced (s) to prepare the block (s) B. Thus, for example, the soft block A may comprise by weight from 40 to 100% styrene and / or acrylate butyl or 2 ethyl hexyl, from 0 to 30% of at least one comonomer chosen from the list defined above and from 1 to 30% of at least one photoactive monomer, the total being 100%.

As regards block B, it comprises at least one photoactive monomer and optionally at least one other monomer copolymerizable with the photoactive monomer. The said other monomer may be chosen from the list of monomers defined above for block A. It may also be a monomer with a cooperative effect. The content by weight of photoactive monomer in block B may range from 5 to 100%.

In a preferred form, the monomer that is copolymerized with the photoactive monomer is a cooperative effect monomer. It is preferably TCLP, PEMA, TCLPa or PEA. Block B comprises, for example by weight, from 10 to 80% of at least one photoactive monomer, from 10 to 80% of at least one cooperative-effect monomer and optionally one or more other comonomers chosen from the previous list (the total doing 100%).

According to the process for preparing the block copolymer, the block B may contain monomer (s) making up the block (s) A. In fact, in the case where the block A is prepared during a first step, the block B may contain monomer residues constituting the block A. Thus, if these residual monomers are not completely polymerized (s) are present in the reaction mixture when initiates the polymerization leading to (x) block (s) B, the block (es) B may comprise monomer (s) initially introduced (s) to prepare the block (s) A. Thus, for example, the block B may comprise in weight of 40 to 100% of active monomer and / or monomer with a cooperative effect, from 0 to 60% of at least one monomer chosen from the list defined above for the synthesis of block A, the total being 100%. As regards the block copolymer of the invention, it comprises at least one soft block A and at least one block B comprising at least one photoactive monomer.

According to NUPAC's 1996 definition of polymer nomenclature, a block copolymer consists of adjacent blocks that are constitutionally different, ie, blocks comprising units derived from different monomers or the same monomer, but according to a composition or a sequential distribution of different patterns. A block copolymer may for example be a diblock, triblock or star copolymer.

Preferably, the block copolymer is such that block (s) A and block (es) B are incompatible, that is to say that they have a Flory interaction parameter. - Huggins χ _AB > 0 at room temperature (parameter well known by those skilled in the art and described in particular in the chemistry and physico-chemistry of polymers, by M. Fontanille and Y. Gnanou, Dunod 2002). This results in a microseparation of phases with the formation of a two-phase structure on a macroscopic scale. The block copolymer is then nanostructured, that is to say that domains are formed whose size is less than 100 nm, preferably between 5 and 50 nm. Nanostructuring has the advantage of leading to a transparent material. In addition, this makes it possible to obtain domains concentrated in chromophores because there is no "dilution" by the block (s) A, which makes it possible to promote the cooperative effect between chromophores (with an increase in the writing speed).

The block copolymer is preferably a triblock copolymer B-A-B 'comprising a central block A connected by covalent bonds to two lateral blocks B and B' (that is to say arranged on each side of the central block A). B and B 'may be the same or different (this type of copolymer is sometimes also noted B-b-A-b-B'). It can also be a triblock copolymer ABA 'comprising a central block B connected by covalent bonds to two lateral blocks A and A (that is to say arranged on each side of the central block B) and which comprise chromophore patterns. A and A 'may be the same or different.

However, according to the process used for the synthesis of the block copolymer, more complex structures can be obtained, for example with a number of blocks greater than or equal to 2, for example 5 blocks, B "-A'-B'- AB, 6 blocks, ... The The synthesized block copolymer can therefore consist of a single structure or a mixture of different structures, more or less complex. The mechanical and optical properties obtained can then vary widely depending on the block copolymer used in the 3D storage material. However, the structuring at the nanoscale obtained by the incompatibility of blocks A and B remains a property common to the various block copolymers which are the subject of the present invention.

Among the ABA 'or BAB' triblock copolymers that can be used in the invention, mention is made more particularly of those for which:

The blocks A and A comprise, as major monomer (s), styrene and / or MMA and / or alkyl acrylate;

The blocks B and B 'comprise, by weight, from 10 to 60% of at least one photoactive monomer, from 10 to 60% of at least one cooperative-effect monomer and optionally a monomer from the preceding list of monomer mentioned for the block A (the total making 100%), which is preferably an alkyl (meth) acrylate, more particularly methyl methacrylate.

The block copolymer may be used alone or in admixture with another polymer which has sufficient transparency in the wavelength range used for writing or reading as well as low birefringence. It can be a thermoplastic, a thermoplastic elastomer or a thermosetting. This characteristic is important for the 3D optical memory technology for which it is necessary for the light ray to reach each layer of the memory without being disturbed. A thermoplastic such as a homo- or copolymer of methyl methacrylate or styrene or a polycarbonate is preferably used. The mixture comprises, by weight, from 50 to 100%, advantageously from 75 to 100%, preferably from 90 to 100%, of the block copolymer, respectively from 0 to 50%, advantageously from 0 to 25%, preferably 5 to 10%. % of the thermoplastic. The mixture is obtained using all the thermoplastic blending techniques known to those skilled in the art. It is preferably extrusion. The block copolymer and / or the mixture of block copolymers may also optionally comprise various additives (antistatic, lubricant, colorant, plasticizer, antioxidant, anti-UV, etc.). Process for obtaining the block copolymer

The block copolymer is obtained using polymerization techniques known to those skilled in the art. One of these polymerization techniques may be anionic polymerization as it is for example taught in the following documents FR 2762604, FR 2761997 and FR 2761995. It may also be the controlled radical polymerization technique which comprises several variants depending on the nature of the control agent that is used. SFRP (Stable Free Radical Polymerization) uses nitroxides as a control agent and can be initiated by alkoxyamines, ATRP (Atom Transfer Radical Polymerization) uses metal complexes as a control agent and is initiated by halogenated agents. RAFT (Reversible Addition Fragmentation Transfer) uses sulfur-containing products such as dithioesters, trithiocarbonates, xanthates or dithiocarbamates. Reference can be made to the general review Matyjaszewski, K. (Ed.), ACS Symposium Series (2003), 854 (Advances in Controlled / Living Radical Polymerization) and the following documents for more details on controlled radical techniques which can be used: FR 2825365, FR 2863618, FR 2802208, FR 2812293, FR 2752238, FR 2752845, US 5763548 and US 5789487.

Controlled radical polymerization with T nitroxide control is the preferred technique for obtaining the block copolymer of the invention. Indeed, this technique does not require working under conditions as severe as the anionic polymerization (that is to say, no moisture, temperature <100 ⁰ C). It also makes it possible to polymerize a wide range of monomers. It can be conducted under various conditions, for example by mass, solvent or dispersed medium such as suspension or emulsion in water.

The nitroxide T is a stable free radical having a group = N-O ", that is to say a group on which is present a single electron. The term "stable free radical" denotes a radical that is so persistent and non-reactive with respect to air and moisture in the ambient air that it can be handled and stored for a much longer period than the majority free radicals (see Accounts of Chemical

Research 1976, 9, 13-19). The stable free radical is thus distinguished from free radicals whose lifetime is ephemeral (from a few milliseconds to a few seconds) as the free radicals derived from the usual initiators of polymerization such as peroxides, hydroperoxides or azo initiators. Free radicals initiating polymerization tend to accelerate polymerization whereas stable free radicals generally tend to slow it down. It can be said that a free radical is stable within the meaning of the present invention if it is not a polymerization initiator and if, under the usual conditions of the invention, the average lifetime of the radical is at least one minute.

The nitroxide T is represented by the structure (IX):

R ₆ - CR ₈

-O '

R ₉ CR ₁₁ Rio (IX) wherein R _6, R7, Rs, R9, R _I O and R ₁₁ denote linear or branched alkyl groups C ₁ -C ₂ O, preferably C ₁ -C ₁₀ such as methyl, ethyl, propyl, butyl, isopropyl, isobutyl, tert-butyl, neopentyl, substituted or unsubstituted, C ₆ -C ₃₀ aryls substituted or unsubstituted by one or more substituents, such as benzyl, aryl (phenyl), cyclic saturated C ₁ -C ₃₀ and wherein the groups R ₆ and R ₉ may be part of an optionally substituted cyclic structure R ₆ -CNC-R ₆ which may be chosen from:

x denoting an integer between 1 and 12.

By way of examples, the following nitroxides can be used:

TEMPO

In a particularly preferred manner, the nitroxides of formula (X) are used in the context of the invention:

• R ₃ and R _b denote identical or different alkyl groups having from 1 to 40 carbon atoms, optionally linked to each other so as to form a ring and optionally substituted with hydroxyl, alkoxy or amino groups,

• R _L designating a monovalent group of molar mass greater than 16 g / mol, preferably greater than 30 g / mol. The group R _L may for example have a molar mass of between 40 and 450 g / mol. It is preferably a phosphorus group of general formula (Xl): wherein Z ₁ and Z ₂ , which may be the same or different, may be selected from alkyl, cycloalkyl, alkoxyl, aryloxyl, aryl, aralkyloxy, perfluoroalkyl, aralkyl and may include from 1 to 20 carbon atoms; Z ₁ and / or Z ₂ may also be a halogen atom such as a chlorine, bromine or fluorine atom.

Advantageously, R _L is a phosphonate group of formula: in which R _c and R _d are two identical or different alkyl groups, optionally linked so as to form a ring, comprising from 1 to 40 carbon atoms, optionally substituted or not by one or more substituents as described above.

In particular, the stable nitroxide radical originates from a molecule which splits into two radicals, one nitroxide, regulator of the polymerization, the other initiator of the polymerization. As a molecule capable of forming in situ the stable nitroxide radical under the effect of a rise in temperature, mention may be made of the BLOCBUILDER ® manufactured and marketed by the Applicant. The R _L group may also comprise at least one aromatic ring such as the phenyl radical or the naphthyl radical, substituted for example by one or more alkyl radicals comprising from 1 to 10 carbon atoms.

The nitroxides of formula (X) are preferred because they make it possible to obtain good control of the radical polymerization of (meth) acrylic monomers. Alkoxyamines of formula (XIII) are preferred:

wherein Z is a multivalent group and o is an integer of 1 to 10 inclusive. Z is a group capable of releasing several radical sites after thermal activation and rupture of the covalent ZT bond. Examples of groups Z are found on pages 15 to 18 of international application WO 2006/061523. Preferably, Z is a divalent group, i.e. the integer o is 2.

In order to obtain a triblock copolymer by means of the controlled radical polymerization technique, it is advantageous to use a difunctional alkoxyamine of formula TZT (that is to say an alkoxyamine of formula (XIII) with o = 2 ). The central block is first prepared by polymerizing with the alkoxyamine the monomer mixture leading to the central block. The polymerization takes place with or without a solvent or in a dispersed medium. The mixture is heated to a temperature above the activation temperature of the alkoxyamine. When the central block is obtained, the monomer (s) leading to the side blocks is added. It is possible that at the end of the preparation of the central block, there remain monomers not completely consumed that we can choose to eliminate or not before the preparation of the side blocks. The removal may for example consist of precipitating in a non-solvent, recovering and drying the central block. If one chooses not to remove the monomers not entirely consumed, they can polymerize with the monomers introduced to prepare the side blocks.

Writing / reading data

The optical principles underlying the present invention are the same as those described in international applications WO 01/73779 and WO 03/070689. The writing is based on the conversion of one isomeric form to another under the effect of a light irradiation. The conversion requires having a chromophore in an excited state, which requires absorption at an energy level E. The absorption of two photons is facilitated by combining the energy of at least two photons of one or more photons. a plurality of light beams (x) having energy levels E ₁ and E ₂ which may be different from E. The two light beams are in the UV, visible or near-infrared range. Preferably, only one light beam is used and the conversion is the result of a two-photon absorption process.

The reading may be based on a linear or non-linear electronic excitation process. The emission spectra of the two isomers are different and the emission is collected using a suitable reading device. A non-linear process such as Raman scattering or a Four Wave Mixing Process ("Four Wave Mixing Process") can be employed.

A small volume element of the 3D memory contains the chromophores in a major isomeric form or else under the other. The volume element therefore contains information stored in a well-defined and localized area of the memory and is characterized by an optical signal different from that of its immediate environment.

About 3D optical memory

The invention also relates to the 3D optical memory (or 3D optical storage unit) comprising the block copolymer or the mixture of block copolymers of the invention and which is used to record (store) the data. A 3D memory is a memory that stores data at any point (defined by three coordinates x, y and z) of the volume of the memory. A 3D memory allows storage of data in several virtual layers (or virtual levels). The volume of the 3D memory is therefore related to the physical volume occupied by it.

This is for example in the form of a plate, square or rectangular, a cube or a disc which comprises the block copolymer of the invention optionally in the form of the mixture as described above. The 3D memory can be obtained by injecting the block copolymer or the block polymer blend. This transformation technique is known to the plasturgists and consists in injecting under pressure the material in the molten state in a mold (in this connection, reference can be made to the Summary of plastics, Nathan, ^4th edition, ISBN 2-12-355352-2, pp. 141 - 156). The material is melted and compressed using an extruder. It is also possible to superpose several layers comprising the block copolymer or the block copolymer mixture of the invention as taught in the international application WO 2006/075329.

Preferably, the 3D optical memory is in the form of a disk which makes it possible to set it in rotation, the writing or reading head being fixed. The disc may be obtained by injection or molding of the block copolymer or the block copolymer mixture if it has the appropriate mechanical characteristics. It can also be obtained by depositing the block copolymer or the copolymer mixture on a rigid and transparent support in the range of wavelengths used for writing and / or reading.

[Examples]

The BLOCBUILDER ^® corresponds to the product of formula:

Example O

Preparing a difunctional dialkoxyamine into a reactor of 250 cm ³ glass delivered by a nitrogen sweep was charged 125 ml of ethanol, 38 g of BlocBuilder ^® and 10 g of diacrylate of 1, 4-butanediol. The reaction mixture is heated at 80 ^° C. for 4 h with stirring (250 rpm). The resulting mixture is then cooled and the ethanol evaporated in vacuo. The resulting solid is formed of a dialkoxyamine which is then used as it is.

Example 1

Preparation of a triblock copolymer P (MeMMA co PEMA) -bP (butyl acrylate st st stene) -bP (MeMMA co PEMA) Step 1 synthesis of the soft block A 98.6 g of dialkoxyamine of the example are introduced under an inert atmosphere 0.660 g of styrene and 1540 g of butyl acrylate in a stirred 3 liter stainless steel reactor. The reaction is conducted at 1 18 ⁰ C for 190 minutes. The resulting reaction product is treated to remove unreacted monomers.

The butyl polyacrylate co styrene obtained is then withdrawn from the reactor. The Tg of the measured block A is -5 ° C.

Step 2: Synthesis of Block B

45 g of block A, 105 g of MeMMA, 105 g of PEMA and 1200 g of toluene are introduced into a 3-liter reactor.

The reaction is carried out at 116 ° C. with stirring for 3 hours. The reaction product is then withdrawn. It corresponds to the expected triblock polymer.

Example 2

Step 1: synthesis of the soft block A

98.6 g of dialkoxyamine of Example 6, 0.660 g of styrene and 1540 g of butyl acrylate are introduced under an inert atmosphere into a stirred 3 liter stainless steel reactor.

The reaction is conducted at 1 18 ⁰ C for 190 minutes.

The resulting reaction product is treated to remove unreacted monomers.

Step 2: synthesis of block B

In a 3-liter reactor, 60 g of Block A are charged with 240 g of MeMMA, 240 g of PEMA and 880 g of toluene. The reaction is carried out at 116 ° C. with stirring for 3 hours.

The reaction product is then withdrawn. It corresponds to the expected triblock copolymer.

Example 3

Preparation of a diblock copolymer P (MeMMA co PEMA) -b-P (butyl acrylate styrene)

Step 1 synthesis of the soft block A

Under an inert atmosphere are introduced 70 g of BlocBuilder ^®, 630 g of styrene and 1470 g of butyl acrylate in a stainless steel 3-liter reactor under stirring. The reaction is carried out at 17 ^° C. for 180 minutes. The resulting reaction product is treated to remove unreacted monomers.

2nd step

In a 3-liter reactor, 20 g of block A, 80 g of MeMMA, 80 g of PEMA and 1100 g of toluene are introduced.

The reaction is carried out at 116 ° C. with stirring for 3 hours. The reaction product is then withdrawn. It corresponds to the expected diblock copolymer.

Example 4: Making Disc

The polymer solutions obtained in Examples 1 to 3 are precipitated in a large quantity of methanol at room temperature, filtered, washed and dried. The product obtained is then shaped by compression-molding at 150 ⁰ C for 10 min to form a disc of 2 cm in diameter and 2 mm thick. The light transmission is greater than 80% over the entire visible range. This disk is then subjected to a static read-write test of data using a suitable laser device. There was a recording of the data on the disc.

Claims

claims

A block copolymer comprising:

At least one soft block A having a T ₉ between -55 ° C. and 0 ^° C., preferably between -40 ^° C. and -1 ° C., and

At least one block B comprising at least one photoactive monomer carrying a photo-isomerizable chromophore of formula (I):

CR-LG-C = CH ₂

I x (I) wherein: • X is H or CH ₃ -;

G denotes -OC (= O) -, -C (= O) -O-, a substituted or unsubstituted phenyl group, or -NR-C (= O) -, NR being connected to L and R being H or a C1-C10 alkyl group;

• L denotes a spacer group; • CR denotes a photo-isomerizable chromophore.

2. Block copolymer according to claim 1, characterized in that the spacer group L is chosen such that G and CR are connected to each other by a sequence of 2 or more atoms which are linked together by covalent bonds.

3. Block copolymer according to one of the preceding claims, characterized in that L is selected from (CRiR ₂ ) _m! O (CRiR ₂ ) _m! (OCRiR ₂ ) _m , (SCRiR ₂ ) _m wherein m is an integer greater than 2, preferably between 2 and 10, R 1 and R ₂ independently denote H, halogen or alkyl or aryl groups.

4. Block copolymer according to one of the preceding claims, characterized in that the chromophore CR is of the diarylalkylene type.

5. block copolymer according to one of the preceding claims, characterized in that the chromophore CR has a recovery <35%, the spectra being recorded on a solution of the chromophore 0.01 M in a vessel of 1 cm of optical passage .

Block copolymer according to one of the preceding claims, characterized in that the Stokes displacement is> 100 nm.

7. Block copolymer according to any one of the preceding claims, characterized in that the photoactive monomer has formula (II): wi Ar ₂ - L-G-C = CH ₂

Ar ₁ W ₂ (H) in which:

Ar ₁ and Ar ₂ denote optionally substituted aryl groups; W ₁ and W ₂ are chosen from the groups H, -CN, -COOH, -COOR ', -OH,

-SO ₂ R ', -NO ₂ , R' being a C ₁ -C ₁₀ alkyl or aryl group.

8. Block copolymer according to claim 7, characterized in that Ar ₁ and Ar ₂ are chosen independently of each other from phenyl, biphenyl, anthracene or phenanthrene, substituted or unsubstituted.

9. Block copolymer according to claim 7, characterized in that the photoactive monomer has the formula (III) or (IV): wi Ar ₂ -L-O-C (= O) - C = CH ₂

Ar ₁ W ₂ (m)

in which :

Ar ₁ and Ar ₂ denote optionally substituted aryl groups;

Block copolymer according to any one of the preceding claims, wherein the chromophore is selected from:

W ₁ and W ₂ being chosen from the groups H, -CN, -COOH, -COOR ', -OH, -SO ₂ R', -NO ₂ , R 'being a C ₁ -C ₁₀ alkyl or aryl group; and each of the two phenyl rings may be optionally substituted.

11. Block copolymer according to claim 10, characterized in that Ar ₁ is a phenyl or biphenyl group and Ar ₂ is a phenyl or biphenyl group, each of the phenyl and / or biphenyl groups may be optionally substituted.

12. Block copolymer according to claim 11, characterized in that W ₁ and W ₂ denote CN, Ar ₂ is a phenyl or biphenyl group, Ar ₁ is a phenyl or biphenyl or biphenyl group substituted by R ₅ O-, R ₅ S -R ₅ denoting an alkyl or aryl group, substituted or unsubstituted.

13. Block copolymer according to claim 7, characterized in that the photoactive monomer is MeAA or MeMMA of formulas:

14. Block copolymer according to any one of claims 1 to 4, characterized in that the chromophore CR comprises a stilbene group, spiropyran, azobenzene, bisazobenzene, trisazobenzene or azoxybenzene.

15. Block copolymer according to any one of the preceding claims, characterized in that the block A has a mass average number M _n > 2000 g / mol, advantageously> 5000 g / mol, preferably> 10000 g / mol, even more preferentially> 50000 g / mol.

16. Block copolymer according to one of the two preceding claims, characterized in that the Tg of the block A is between -30 ⁰ C and -3 ° C.

17. Block copolymer according to one of the preceding claims, characterized in that the soft block A is obtained from the polymerization of at least one vinyl, vinylidene, diene, olefinic, allylic or (meth) acrylic monomer.

18. Block copolymer according to claim 16, characterized in that the block A comprises, as majority monomer (s), butyl acrylate or 2-ethylhexyl acrylate.

19. Block copolymer according to one of the preceding claims, characterized in that the block B comprises at least one photoactive monomer and optionally at least one other monomer copolymerizable with the photoactive monomer.

20. Block copolymer according to one of claims 17 to 19, characterized in that the block B further comprises a cooperative effect monomer of formula

(IX):

Ar ₃ -LG-C = CH ₂ I x (IX) in which:

X, G and L are as defined in any one of claims 2 to 4;

Ar ₃ denotes an aromatic group which may or may not be substituted by one or more substituents.

21. Block copolymer according to claim 20, characterized in that the substituent is chosen from:

(i) halogens, preferably chlorine;

(ii) -COOY, -CONYY ', -OY, -SY or -C (= O) Y, Y and Y' denoting an H or C1-C10 alkyl group

(iii) - CYY'Y ", Y ₁ Y ', Y" denoting an H or C ₁ -C ₁₀ alkyl group

22. Block copolymer according to one of claims 20 or 21, characterized in that Ar ₃ is a phenyl group.

23. Block copolymer according to claim 20, characterized in that the monomer with a cooperative effect is chosen from:

PEMA PPMA

PEA PPA) ₃ - OC (= O) -CH = CH ₂ TCLPa

24. Block copolymer according to one of claims 20 to 25, characterized in that the block B comprises by weight of 10 to 80% of at least one photoactive monomer, from 10 to 80% of at least one monomer to cooperative effect and possibly one or more other monomers.

25. Blend of a block copolymer as defined in any one of the preceding claims and a polymer which is a thermoplastic, a thermoplastic elastomer or a thermosetting.

26. The blend of claim 25, comprising by weight of 50 to 100%, advantageously from 75 to 100%, preferably from 90 to 100%, of the block copolymer for 0 to 50%, advantageously from 0 to 25%. preferably 5 to 10% of the thermoplastic polymer or thermoplastic elastomer or thermosetting.

27. The blend of claim 25 or 26, wherein the thermoplastic polymer is a homo- or copolymer of methyl methacrylate or a polycarbonate.

28. 3D optical memory comprising a block copolymer as defined in any one of claims 1 to 24 or a mixture as defined in any one of claims 25 to 27.

29. The optical 3D memory according to claim 28, in the form of a plate, square or rectangular, a cube or a disc.

30. Use of a block copolymer as defined in any one of claims 1 to 24 or a mixture as defined in any one of claims 25 to 27, for performing optical data storage.

31. Use of a block copolymer as defined in any one of claims 1 to 24 or a mixture as defined in any one of claims 25 to 27 as a 3D optical memory.